class Solution {
public:
    int numDistinct(string s, string t) {
        int n = s.size(), m = t.size();
        int mod = 1e9 + 7;
        vector<vector<int>> dp(n + 1, vector<int>(m + 1));
        for (int i = 0; i <= n; i++)
            dp[i][0] = 1;

        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= m; j++)
            {
                dp[i][j] = dp[i - 1][j];
                if (s[i - 1] == t[j - 1])
                    dp[i][j] = (dp[i - 1][j - 1] + dp[i][j]) % mod;
            }
        }
        return dp[n][m];
    }
};